||Statistical physics is an unfinished and highly active part of physics. We do not have the theoretical framework in which to even attempt to describe highly irreversible processes such as fracture. Many types of nonlinear systems that lead to complicated pattern formation processes, the properties of granular media, earthquakes, friction and many other systems are beyond our present understanding and theoretical tools.
In the study of these and other macroscopic systems we build on the established conceptual framework of thermodynamics and statistical physics. Thermodynamics, put into its formal and phenomenological form by Clausius, is a theory of impressive range of validity. Thermodynamics describes all systems form classical gases and liquids, through quantum systems such as superconductors and nuclear matter, to black holes and elementary particles in the early universe in exactly the same form as they were originally formulated.1
Statistical physics, on the other hand gives a rational understanding of Thermodynamics in terms of microscopic particles and their interactions. Statistical physics allows not only the calculation of the temperature dependence of thermodynamics quantities, such as the specific heats of solids for instance, but also of transport properties, the conduction of heat and electricity for example. Moreover, statistical physics in its modern form has given us a complete understanding of second-order phase transitions, and with Wilson's Renor-malization Group theory we may calculate the scaling exponents observed in experiments on phase transitions.
However, the field of statistical physics is in a phase of rapid change. New ideas and concepts permit a fresh approach to old problems. With new concepts we look for features ignored in previous experiments and find exciting results. Key words are deterministic chaos, fractals, self-organized criticality (SOC), turbulence and intermitency. These words represent large fields of study which have changed how we view Nature.